The present invention relates to golf clubs, and more particularly relates to a golf club head having an adjustable loft.
In golf, clubs are used having varying loft angles to impart greater or lesser distance or height to the ball. Drivers having a slight angle from the vertical are used to drive the ball a great distance horizontally with a relatively flat trajectory. A putter with virtually no loft angle is used on the green itself. At intermediate distances, irons having varying loft angles measured from the vertical are used. Typically, larger loft angles are used for shorter distances. Most golfers use up to 14 clubs (limited by rule) with varying lofts at approximately four-degree increments. The need for multiple clubs creates a number of disadvantages, such as the high cost of a complete or partial set, and the need for transportation of a bulky and heavy set of clubs, both to and on the course.
A number of adjustable golf clubs have been developed with the object of reducing the number of clubs required. Many designs have used one or more sets of teeth or splines to key-in the various desired loft angles. Adjustable club heads using splined shafts are exemplified by U.S. Pat. Nos. 1,219,417 to Vories; 2,305,270 to Nilson; 1,429,569 to Craig; 2,571,970 to Verderber; 3,601,399 to Agens et al; and 4,878,666 to Hosoda. Clubs employing multiple toothed rings for vernier adjustment are exemplified by U.S. Pat. Nos. 2,882,053 to Lorthiois; and 3,840,231 and 5,538,245, both to Moore. A ratcheting vernier adjustment is taught in U.S. Pat. No. 5,133,553 to Divnick. Sealed containers having permeable elastomeric sheets sealed together and inflated with a gas having low permeability therethrough is taught in U.S. Pat. No. 4,287,250, to Rudy. The teachings of the patents cited above are entirely incorporated herein by reference.
As the impact of the club head with the ball generates large forces and torques acting in unpredictable directions, various auxiliary fastening devices such as nuts, screws and levers have been used to lock-up the head so that the loft angle does not accidentally change during use. These auxiliary devices are undesirable, as they detract from the enjoyment of the game. They are also prone to failure with repeated use, due to over or under tightening, and to contamination or corrosion.
It would be desirable for a club to be self-locking, so that no auxiliary devices would be needed. It would also be desirable that the concentration of the golfer not be broken by the need to make complicated adjustments to the club. And it would be most desirable that the loft angle be changeable in one continuous and smooth motion by the golfer.
The present invention provides a uniquely simple solution to the problems associated with adjustable golf clubs, and does so without requiring that the golfer remember arcane and complicated adjustment procedures. Rather, the instant invention provides a perfectly natural and aesthetically desirable look and feel for both the club and the adjustment thereof, while also enhancing the technical performance of the club.
An important feature of an adjustable club is that the loft angle, once set, does not change during use. First of all, if the equipment is not reliable, the player""s lack of confidence can negatively effect his game, and secondly, a club head that moves under impact conditions can damage the adjustment mechanism, and ruin the club. In the present invention, the head, once set at the desired loft angle, is hydrodynamicly locked-up, and cannot move into an unlocked position due to the collision of the club with a ball. This lock-up is achieved automatically during impact conditions.
As golf is an aesthetic game, it is important that the head adjusts smoothly, substantially without noise or snap-back, and without requiring tools. It is also important that the adjustment is easily achieved without the need for calculation on the part of the golfer.
The present invention accomplishes the above and other objectives by dividing the working volume within the adjustable club head into at least three chambers: first and second chambers filled with an incompressible fluid, and a third chamber filled with a compressible fluid.
The working volume within the club head comprises a splined (toothed) pivot shaft which mates with a splined inner cylinder surface fixed within the adjustable club head. It is desirable that both the exterior splined surface of the pivot shaft and the interior splined surface of the cylinder are segmented, with gaps therebetween, so as to reduce the total axial motion required to de-couple the splines while providing sufficient tooth area to resist rotation. When not being adjusted, the splines are aligned so as to prevent relative rotation, and the pressure of the gaseous fluid within the third chamber maintains this coupled axial alignment. The third chamber pressurizes the second liquid filled chambers by means of a flexible diaphragm or floating piston therebetween. The first chamber is pressurized by means of a fluid conduit between the first and second chambers, so that, at rest, the pressures in all three chambers are equal (and above atmospheric). Most typically, all chambers are coaxial with the pivot shaft, with the second chamber between the first and third chambers.
The conduit between the first and second chambers restricts the rate of fluid flow between them. This results in a small pressure build-up within the first chamber relative to the second, resulting in a resistance and a smooth axial motion of the club head on the pivot shaft as the two are pressed together by the golfer during adjustment. During a stroke, while under impact conditions, the pressure build-up is much greater than it is during adjustment, and tends to resist axial motion and the resultant de-coupling of the splines. By way of example only, and not limitation, if one pound of force applied for one second is necessary to de-couple the splines during adjustment (this is the hydrodynamic force generated by fluid flow in the conduit only, and neglects the gas pressure in the third chamber, which must also be overcome), then, during an impact of the golf head with a ball lasting only one millisecond, a million pounds of force would be required to move the fluid through the conduit and thereby de-couple the splines. The force required is so much greater because the hydraulic force generated varies inversely with the square of the time period involved. If the impact period is three orders of magnitude smaller than the adjustment period, then the de-coupling force required will be six orders of magnitude greater. This force resisting de-coupling is so large that the head remains effectively locked-up during the brief period of impact.